1. Field of the Invention
The present invention relates to electric irons, and more particularly to thermostatic controls for electric irons.
2. Description of Prior Art
A typical iron control consists of a bimetal actuator which actuates a microswitch which controls the electrical supply to the heating element. The bimetal is usually mounted by a screw on a boss on the sole plate, and is heated by conduction of heat from the sole plate. This results in a thermal lag which leads to the iron temperature overshooting its nominal, set temperature when heating up particularly on initial turn on. This is obviously undesirable as clothing may be damaged. Also, the sole plate temperature undershoots when the iron is cooling down before power is resupplied to the element. Thus the temperature variation of the sole plate is considerably larger than that measured for the thermostat alone.
Furthermore, depending on where the bimetal is mounted on the sole plate, it may experience a higher or lower temperature than the average sole plate temperature. For example if the bimetal is too close to the element, it will experience too high a temperature and the control will therefore initially trip at lower sole plate temperatures than desired and clothing will not be properly ironed.
Various steps have been taken to try to improve such controls, particularly with the advent of cordless irons where high wattages are employed to quickly bring the iron back to temperature when it is replaced on its stand, and where the problems of temperature overshoot are therefore greater.
One approach has been to introduce electronic controls. However these controls are inherently unsuitable for high temperature and high humidity conditions which are typical in steam irons. Other attempts have been made to improve the performance of the bimetals, but these have not been particularly successful.